This application claims priority under 35 U.S.C. xc2xa7xc2xa7 119 and/or 365 to Patent Application Serial No. 0102582-2 filed in Sweden on Aug. 9, 2001, the entire content of which is incorporated herein by reference.
This invention relates to a rotatable cutting tool of the type that comprises a basic body, rotatable around a geometric axis, and a cutting insert that is mountable in a seat formed in the basic body, which seat has two supports, viz. a bottom surface against which a bottom side of the cutting insert is pressable and a radial support against which a side surface of the cutting insert is pressable in order to fix the cutting insert in respect to radial and/or tangential forces. Fixing of the cutting insert in respect of axial forces is guaranteed by a screw insertable in a through hole in the cutting insert, which screw has a head countersinkable in the cutting insert, and a shaft that includes on the one hand a lower male thread for engagement with a female thread in a lower part of a second hole formed in the holder, which opens in a port in the bottom surface of the seat, and on the other hand an upper, rotationally symmetrical, non-threaded portion that is locatable in an upper bore that extends between the female thread and the port of the second hole.
A cutting tool of the above generally mentioned kind is previously known from Deiss et al. U.S. Pat. No. 5,542,793. Characteristic of this tool, which is exemplified in the form of a cylindrical cutter, is that the seats for the cutting inserts lack particular axial supports. The axial forces, which act on the individual cutting insert, are resisted (absorbed) by the screw that has the purpose of clamping the cutting insert in the seat. The upper portion of the shaft of the screw is cylindrical and manufactured having an outer diameter which is slightly smaller than the inner diameter of a likewise cylindrical bore of the holder in which the upper shaft portion is received in order to fix the individual cutting insert in a position that is as exactly geometrically defined as possible on tightening the screw. In this way, the upper cylindrical portion of the screw shaft is provided with a very tight fit in relation to the interior of the bore. This narrow fit is present all the way from the port (or mouth) of the bore to the place where the bore transforms into the female thread. Upwards from the port, the cylindrical shaft portion of the screw extends a short distance up to a place where the same transforms into a conical surface formed on the head, which is tightened against a conical surface in the through hole in the cutting insert. Between this conical surface and the bottom side of the cutting insert, the through-hole includes a lower hole portion which has a considerably greater inner diameter than the outer diameter of the cylindrical shaft portion. The center axis for the second hole formed in the basic body, i.e., the hole that includes the female thread together with the cylindrical bore, and the center axis for the through-hole in the cutting insert, are somewhat displaced in relation to each other in the radial direction, more precisely with the purpose of enabling the upper part of the screw to bend and forcefully press a side surface of the cutting insert against a radial support formed in the basic body, on tightening of the screw.
A disadvantage of the problem-solving presented in U.S. Pat. No. 5,542,793 is however on one hand precisely the fact that the shaft portion of the screw has a narrow fit all the way along the cylindrical bore in the hole in the basic body, and on the other hand the fact that the protruding shaft portion that extends between the head of the screw and the bottom surface of the seat is comparatively short. Therefore, the distance along which the upper part of the screw may bend, and which is determined by the distance between the head and the bottom surface of the seat becomes very limited. This may in practice have harmful consequences, e.g. in such a way that the upper part of the screw is cracked or damaged in another way on tightening. Furthermore, the smooth surface of the bore may be damaged and deformed, above all in connection to the port, something which in turn may result in the ability of the screw to axially fix the cutting insert in an exact way being lost.
Because of varying production tolerances, the actual contact point between the shaft of the screw and said bore may furthermore vary in an uncontrolled way. At one time, the contact point or surface may be located in the immediate vicinity of the port and at other times, it may be located deeper down in the hole.
The present invention aims at obviating the above-mentioned disadvantages of the cutting tool according to U.S. Pat. No. 5,542,793 and at providing an improved cutting tool. Thus, a primary aim of the invention is to provide a cutting tool having at least one replaceable cutting insert that may be fixed in an exact position by means of a radial support and a fixing screw, i.e., without particular axial supports, and to, in relation hereby, guarantee on the one hand that the contact point or the contact place between the screw and the hole in the basic body is always located in a repeatable and well-defined way, and on the other hand that neither the screw nor the receiving hole is damaged in connection with mounting and dismounting, respectively, of the cutting insert. An additional aim is to provide a cutting tool, the cutting insert of which is pressed and retained against the radial support in a reliable way.
According to the invention, at least the primary aim is attained by a rotatable tool which comprises a rotatable basic body defining an axis of rotation. The basic body forms a seat configured to receive a cutting insert. The seat has a bottom surface and a radial support upstanding from the bottom surface. The radial support is arranged to resist forces acting in a radial direction with respect to the axis of rotation. The bottom surface includes a screw-receiving hole which intersects the bottom surface to form a port. The screw-receiving hole includes a female screw-threaded portion spaced form the port by a non-threaded portion. A fastening screw is provided for securing the cutting insert to the basic body. The screw includes a shaft having at one end thereof a male screw thread connectable to the female screw-threaded portion, and at an opposite end thereof a head. The shaft further includes a non-threaded portion disposed between the male screw thread and the head and sized to be received in the non-threaded portion of the screw-receiving hole. The port and the non-threaded portion of the screw-receiving hole have a non-circular shape that is elongated generally in the radial direction to accommodate bending deflection of the non-threaded portion of the screw in that generally radial direction.